Field of the Invention
The present invention relates to a mobile communication system and carrier measurement method thereof and, in particular, to a mobile communication system including base stations and terminals and a method for terminal capable of carrier aggregation to manage carriers using the information included in the UE-specific message received from the base station in the system.
Description of the Related Art
Mobile communication systems have developed to provide the subscribers with voice communication services on the move. With the advance of technologies, the mobile communications have been evolved to support high speed data communication services as well as the standard voice communication services. Recently, as one of the next generation mobile communication system, Long Term Evolution (LTE) is on the standardization by the 3rd Generation Partnership Project (3GPP). LTE is a technology designed to provide high speed packet-based communication of up to 100 Mbps and standardized almost completely now with the aim at commercial deployment around 2010 timeframe. Meanwhile, unlike the voice service, the resource to be allocated for data service is determined according to the data amount to be transmitted and the channel condition. Accordingly, in the wireless communication system such as mobile communication system, a scheduler allocates the transmission resource in consideration of the resource amount for transmission, channel condition, and data amount. This is also the case in the LTE as one of next generation mobile communication systems, and the scheduler located at the base station manages and allocates radio transmission resource.
Recently, the discussions are focused on the LTE-Advanced (LTE-A) for increasing data rate with the integration of novel technologies into the LTE system. One of the representative novel technologies is Carrier Aggregation (CA). CA is a technique to aggregate multiple uplink or downlink carriers. With the CA technique, it is possible to increase the data rate a capacity of the terminal by allocating resources on multiple carriers.
FIG. 1 is a diagram illustrating the architecture of an legacy LTE or LTE-A system.
Referring to FIG. 1, the radio access network of an LTE/LTE-A system includes evolved Node Bs (eNBs) 105, 110, 115, and 120, a Mobility Management Entity (MME) 125, and a Serving-Gateway (S-GW) 130. The User Equipment (hereinafter, referred to as UE) 135 connects to an external network via eNBs 105, 110, 115, and 120 and the S-GW 130. The eNBs 105, 110, 115, and 120 correspond to legacy node Bs of Universal Mobile Communications System (UMTS). The eNBs 105, 110, 115, and 120 allow the UE to establish a radio link and are responsible for complicated functions as compared to the legacy node B.
In the LTE system, all the user traffic including real time services such as Voice over Internet Protocol (VoIP) are provided through a shared channel and thus there is a need of a device which is located in the eNB to schedule data based on the state information such as UE buffer conditions, power headroom state, and channel state. Typically, one eNB controls a plurality of cells.
In order to secure the data rate of up to 100 Mbps, the LTE system adopts Orthogonal Frequency Division Multiplexing (OFDM) as a radio access technology on up to 20 MHz bandwidth. Also, the LTE system adopts Adaptive Modulation and Coding (AMC) to determine the modulation scheme and channel coding rate in adaptation to the channel condition of the UE.
The S-GW 130 is an entity to provide data bearers so as to establish and release data bearers under the control of the MME 125. MME 125 is responsible for various control functions and connected to a plurality of eNBs 105, 110, 115, and 120.
FIG. 2 is a diagram illustrating a carriers aggregated for a UE according to the conventional technology.
Referring to FIG. 2, an eNB performs transmission and reception on multiple carriers of different bands in general. For example, suppose the downlink carrier_1 201 having center frequency F1 and bandwidth of BW1, the downlink carrier_2 203 having center frequency F2 and bandwidth of BW2, and the downlink carrier_3 205 having center frequency F3 and bandwidth of BW3. In this case, unlike the conventional UE capable of receiving data on only one carrier, the UE capable of carrier aggregation can receive data on multiple carriers simultaneously.
This means that, in FIG. 2, the UE is capable of receiving data on the downlink carrier_1 201, downlink carrier_2 203, and downlink carrier_3 205 simultaneously. Likewise, the conventional UE is capable of transmitting data on only one carrier. However, the UE capable of carrier aggregation can transmit data on the uplink carrier_1 211, uplink carrier_2 213, and uplink carrier_3 215 simultaneously.
Accordingly, the eNB is capable of allocating more carriers to the UE capable of carrier aggregation according to conditions so as to increase downlink/uplink transmission capacity/data rate of the UE. Assuming that a cell consists of one downlink carrier and one uplink carrier and one uplink carrier in the conventional concept, the carrier aggregation can be understood as if the UE transmits/receives data through multiple cells simultaneously. With the use of carrier aggregation, the peak data rate expected in a cell increases in proportion to the number of aggregated carriers.
FIG. 3 is a diagram illustrating a measurement method of the conventional UE capable of carrier aggregation.
Referring to FIG. 3, the downlink carrier_1 301 having center frequency F1 and bandwidth of BW1, the downlink carrier_2 303 having center frequency F2 and bandwidth of BW2, and the downlink carrier_3 305 having center frequency F3 and bandwidth of BW3 are configured to be aggregated by the eNB. It is assumed that, among the configured carriers, the downlink carrier_1 301 and the downlink carrier_2 303 are activated carriers and the downlink carrier_3 305 is deactivated carrier. The carrier aggregation configuration is for the eNB to configure the candidate carriers available for carrier aggregation based on the UE capability information and notify the UE of the configuration. The activation/deactivation of configured carriers is to select the carriers to be used for data transmission/reception among the candidate carriers and activate the selected carriers or to select the carriers not to be used for data transmission/reception and deactivate the selected carriers.
For example, the carrier activation can operate in such a way that, when downlink or uplink data occurs actually, the eNB selects the carriers to be used for data transmission/reception among the configured aggregation candidate carriers based on the size of data to be transmitted, radio channel condition, load state of the cell, etc. and notifies the UE of the selected carriers. The carrier deactivation also can operate in the same principle as above.
In FIG. 3, if the downlink carrier_1 301 and the downlink carrier_2 303 are activated, the UE regards that the Radio Frequency (RF) chain_A 311 and RF chain_B 313 operate; and if the downlink carrier_3 305 is activated, the UE regards that the RF chain_C 315 operates. Since the downlink carrier_1 301 and the downlink carrier_2 303 are activated to receive data, the UE maintains the activation of the RF chain_A 311 and RF chain_B 313 for channel measurement on the downlink channel and receiving scheduling information. This means that the UE is capable of performing measurement on the downlink carrier_1 301 and downlink carrier_2 303 without UE's extra power waste.